Face-to-face conversation is usually recognized as the preferred form of human communication. Therefore, a goal of videoconferencing systems is to achieve communication as close as possible to real face-to-face conversation.
Typical video conferencing systems include a display screen and a camera for each site. During video conferencing, the user(s) of a first site observes an image of the second site on the display screen. At the same time, an image of the first site is captured by the camera and projected on the display screen at the second site. The user(s) at the second site observes the image of the first site on the second screen while a camera at the second site simultaneously captures an image of the second site and projects that image upon the screen at the first site.
In the prior art, the projector and the camera associated with the same site operate on different optical paths. When a user at the first site is looking at the image of the second site on the first screen, he/she will be looking away from the camera. For example, consider a video conferencing system that uses a conventional monitor as the display device and a camera mounted on the side, top or bottom of the monitor housing. Because of the closeness of the user to the monitor and the camera being positioned at the periphery of the monitor's display screen, the perspective or angle at which the image of the user is captured is not optimum and the image captured shows the user as looking away from the camera. Thus, the first camera receives an image of the first user that is indirect. As the image from the first camera is projected onto the second screen, the second user also sees an indirect image of the first user (i.e., the second user sees the first user's image as looking away from the line of sight of the second user), and thus there is no “eye contact” between users. Only when the first user is looking directly at the camera (and not at the image of the second user upon the first screen) will there be eye contact between the second user (looking at the second screen) and the first user (looking into the camera). However, users rarely, if ever, change their head position and eye contact to focus on the camera instead of the display, and even when they do, such adjustments in user head position are not natural and require significant concentration and effort. Such prior art systems are problematic because of their inability to capture a direct, full-face image of the user. In summary, there is never a time when both users are looking directly at each other, seeing full-face images upon the screen and having eye contact.
U.S. Pat. No. 5,400,069 discloses a videoconferencing system providing eye contact by means of a special purposed back projection screen. Both projector and camera are positioned behind the screen. The screen is simultaneously translucent with respect to the projector and transparent with respect to the camera and includes segments that discriminate between projected light and light to be captured by the camera based upon polarization or angle. Light from the opposite side of the camera and projector side, e.g. reflected light from the participants, is passed and vertical polarized through the screen, and captured by the camera. Light from the projector reflected on the screen is horizontal polarized, and will not be captured by the camera, because it allows absorption of vertical polarized light only. Thus, participants looking at the projected picture on the screen will also seem to look at the camera behind the screen, and eye contact will be established.
However, U.S. Pat. No. 5,400,069 requires a tailored and back projected screen. Front projections on a simple screen or even on a wall are today extensively adapted as a preferred solution for displaying presentations and information to a group of people in a designed meeting room.